According to the Energy Information Administration (EIA), global consumption of petroleum and other liquid fuels was 92.4 million barrels per day in the year of 2014, and vehicles consumed about 50% of them. As a result, a great amount of emitted gases such as carbon dioxide, NOx, greatly polluted our environment. Because of the development of the automotive industry, particularly in the developing countries, more vehicles have been manufactured. Accordingly the consumption of petroleum and other liquid fuels such as gasoline and diesel is increasing,
The combustion efficiency of fuels in internal combustion engines affects the consumption of fuels and gas emission. In a new internal combustion engine, the combustion efficiency is normally 68%-75%. However in an older engine the efficiency may drop to 50%-55% or lower. To boost the fuel combustion efficacy, many techniques have been developed in last decades. These developments include two main aspects: (1) the optimization of engine systems, for example, optimization of gasoline supply systems, atomizing systems, and computerized air/gas ratio injection, etc. (2) to maintain the fuel supply system in good conditions and to improve properties of fuels in engines to provide better combustion. This can mainly be done by addition of additives to the fuels. The additives include various types of cleansing agents or cleaners, combustion boosters, etc. Water based microemulsion is a typical fuel additive for this purpose. The introduction of water to gasoline was found to reduce emission of particulates by 20%-60% and reduce formation of NOx by 10%-50%. This is attributed to a lower combustion temperature and a so-called “micro-explosion” in engines which disperses fuel droplets by explosive vaporization, and atomizes the fuel effectively. Most additives were comprised of hydrocarbon fuel, water, various alcohols and surfactants. For example, U.S. Pat. No. 5,004,479 to Schon et al discloses a microemulsion fuel comprised of gasoline, methanol, water, and a surfactant blend having a hydrophilic-lipophilic balance value of 3 to about 4.5. U.S. Pat. No. 4,083,698 to Wenzel et al describes fuel compositions which are water-in-oil emulsions and comprise a hydrocarbon fuel such as gasoline or diesel fuel, water, a water-soluble alcohol such as methanol, ethanol or isporpoanol, and a combination of surface-active agents. U.S. Pat. No. 4,451,265 to Schwab describes microemulsion fuel compositions prepared from diesel fuel, water, lower water-miscible alcohols and a surfactant system comprising N,N-dimethyl ethanol amine and a long-chain fatty acid. U.S. Pat. No. 4,451,267 to Schwab et al claims microemulsions prepared from vegetable oil, a C1-C3 alcohol, water and a lower trialkyl amine surfactant, and discloses the optional addition of 1-butanol as a cosurfactant for the purpose of lowering both the viscosity and the solidification temperature of the microemulsion.
Instability of the microemulsion fuel compositions described above has been a disadvantage under conditions to which the fuels have been exposed. Incorporated water will separate, causing problems in storage reservoirs, such as corrosion and bacterial growth. Moreover, water droplets become entrained in filters causing swelling and distortion, yielding unexpected blockage of the supply system from the reservoir, clogging of pumps, etc. The water droplets also form ice crystals in cold weather, causing frosting and blockage of engines.
To improve the stability of the microemulsion, many techniques have been proposed. For example, U.S. Pat. No. 4,744,796 to Hazbun et al proposed a method of improving the stability by adding a cosurfactant combining tertiary butyl alcohol and an ionic or nonionic surfactant. U.S. Pat. No. 5,004,479 to Schon et al disclosed a microemulson using methanol and a fatty acid partially neutralized by a nitrogenous base.
Another factor affecting the stability of the microemulsion is the amount of the water incorporated. In prior art, a water content of 10,000 to 400,000 parts per million (ppm) in the fuel is generally accepted as necessary to achieve any worthwhile improvement in combustion. However, in order to achieve even short term fuel emulsion stability at the high water contents, significantly large quantities of expensive emulsifying surfactants are required (typically 5,000 to 200,000 ppm). The surfactants at a high cost make fuel emulsions with high water content unsuitable for commercial applications. U.S. Pat. No. 4,396,400 to Grangette et al claims that 1,000 ppm of emulsified water with 500 ppm of surfactant gives the optimum improvement. In fact, 500 ppm of surfactant would still be too expensive for commercial applications. Grangette et al also discloses that it is possible to produce “ultra-low” water content fuel emulsions by adding 100 ppm of water, but employing only 25 ppm of a single “crude” surfactant. With so much water and so little surfactant, the resulting fuel emulsion would not be stable enough for commercial applications.
It is known that a large amount of water can improve combustion efficiency and reduce emissions. However, increased water content adversely affects the stability. Hicks et al, in U.S. Pat. Pub. No. 2002/0095,859A1, proposed a way to improve the fuel combustion keeping a good stability. The improved combustion and efficiency can be achieved by adding as little of the composition as needed to result in 5 to 95 ppm of water in the hydrocarbon fuel. Stability of this low water content of microemulsion fuel is achieved with use of surfactant/water ratios at 8:1 to 0.5:1, preferably 3.0:1 to 1.0:1, and most preferably 2.5:1. The resulting microemulsion fuel exhibits improved fuel economy and reduced exhaust emission. U.S. Pat. No. 7,887,604B1 to Hicks et al proposed another way to reduce the amount of water in the fuel microemulsion. U.S. Pat. No. 4,608,057 to Davis et al provides another method to modify hazed water gasoline into stable gasoline additive by blending the haze fuel with nonionic surfactant made from an alkanoic acid derivative. In U.S. Pat. No. 4,477,258, Lepain proposes a method to create stable water-in-oil type diesel fuel emulsion by introducing a mixture of methanol and ethanol and water soluble, ethoxylated, non-ionic surfactant.
Despite the improved ability achieved by a lot of efforts in the prior art, the efficiency of these microemulsions depend on water content. In addition, they are mixtures containing a fuel, either diesel or gasoline, which could possess safety and corrosion issue during fuel storage. Therefore, there is a need to develop an additive with higher efficiency, safety and stability to overcome the problems.
The following patents are cited:
U.S. Patents:
5,004,479Schon et al4,083,698Wenzel et al4,451,265Schwab4,451,267Schwab et al4,744,796Hazbun et al4,396,400Grangette et al7,887,604B1Hicks et al4,608,057Davis, et al4,477,258Lepain2002/0095,859A1Hicks et al